U.S. patent number 3,925,101 [Application Number 05/539,184] was granted by the patent office on 1975-12-09 for electric primary cell in which the positive active material is silver chromate.
This patent grant is currently assigned to SAFT-Societe des Accumulateurs Fixes et de Traction. Invention is credited to Alfred Brych, Gerard Lehmann.
United States Patent |
3,925,101 |
Lehmann , et al. |
December 9, 1975 |
Electric primary cell in which the positive active material is
silver chromate
Abstract
The invention relates to alkaline metal (e.g. Li) and silver
chromate primary cells. It provides for use as a material for the
positive casing of such a primary cell, stainless steel containing
at least 11% of chromium, or up to about 17% chromium, or about 18%
chromium with about 9% nickel, all percentages being by weight.
With such positive casing, a corrosion of the casing during cell
storage or discharge is delayed considerably.
Inventors: |
Lehmann; Gerard
(Chasseneuil-du-Poitou, FR), Brych; Alfred
(Chasseneuil-du-Poitou, FR) |
Assignee: |
SAFT-Societe des Accumulateurs
Fixes et de Traction (Romainville, FR)
|
Family
ID: |
9134678 |
Appl.
No.: |
05/539,184 |
Filed: |
January 7, 1975 |
Foreign Application Priority Data
|
|
|
|
|
Feb 8, 1974 [FR] |
|
|
74.04280 |
|
Current U.S.
Class: |
429/223; 429/199;
429/221; 429/219; 429/231.5 |
Current CPC
Class: |
H01M
6/16 (20130101); H01M 50/545 (20210101); H01M
50/116 (20210101) |
Current International
Class: |
H01M
6/16 (20060101); H01M 2/02 (20060101); H01M
006/00 () |
Field of
Search: |
;136/6LN,1R,166 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kaplan; G. L.
Assistant Examiner: Lefevour; C. F.
Attorney, Agent or Firm: Kenyon & Kenyon Reilly Carr
& Chapin
Claims
What is claimed is:
1. In an electric primary cell whose components comprise as
positive active material silver chromate, as negative active
material an alkaline metal, and as electrolyte a solution of a salt
in an aprotic solvent and wherein the said components are enclosed
in a casing comprising two parts electrically insulated from each
other and containing respectively the negative active material and
the positive active material, and said parts each comprising at
least a metallic portion acting respectively as the positive and
negative terminals of the cell, said cell being characterized in
that the metallic portion of the positive part of the casing is
made of stainless steel containing at least 11% by weight of
chromium.
2. In a primary cell according to claim 1, said steel of said
positive part besides containing chromium, also contains
nickel.
3. In a primary cell according to claim 1, the proportion of
chromium contained in said positive part is about 17% by
weight.
4. In a primary cell according to claim 2, the proportion of
chromium contained in said positive part is about 18% and the
proportion of nickel contained therein is about 9% both percentages
being by weight.
5. A primary electric cell comprising a positive electrode whose
active material is silver chromate, a negative electrode whose
active material is lithium, an electrolyte comprising a solution of
a salt in aprotic solvent, a separator between said positive and
negative electrodes, a casing comprising two parts respectively
containing said negative and positive electrodes, means for
electrically insulating said two parts from each other and
sealingly enclosing said electrolyte, separator and electrodes in
said casing, that one of said casing parts containing said silver
chromate being of stainless steel with at least 11% by weight of
chromium content.
Description
BACKGROUND AND BRIEF SUMMARY OF INVENTION
The present invention concerns electric primary cells having high
specific energy and, more particularly, alkaline metal (preferably
lithium), silver chromate primary cells having an electrolyte whose
solvent is aprotic. These primary cells have a very high open
circuit voltage (greater than 3 volts) and the highly positive
reactive material (silver chromate) has a corrosive effect on the
part of the casing which contains it. Now, the use of primary cells
in watches, for example, requires cell preservation both during
long storage periods and throughout a long discharge period, e. g.
a year or more.
It has been recommended that the positive part of the casing be
prepared of nickel-plated steel. Indeed, nickel is a substance
which will withstand the corrosive effect of silver chromate in the
conditions in which the latter is used. However, the least defect
in the nickel-plating is transformed into a deep crack after a few
months of storage and permits the occurence of corrosive action on
said casing via said crack.
The use of pure nickel for the positve part of the casing is too
expensive a solution for that problem. Moreover, nickel is a
relatively soft metal and its crimping during cell assembly crushes
the edges and is likely to cause leakage.
An object of the present invention is to overcome that disadvantage
and to provide a positive part of the casing which is not very
expensive and withstands corrosion during very long cell storage
and discharge periods.
Another object of the present invention is the provision of an
electric primary cell in which the positive active material is
silver chromate, the negative active material is an alkaline metal,
preferably lithium and the electrolyte is a solution of a salt in
an aprotic solvent and in which the active components are enclosed
in a casing made of two electrically insulated parts, containing
respectively the negative active material and the positive active
material and each comprising at least a metallic portion acting
respectively as the positive and negative terminals of the cell. In
such a cell, the invention is characterized in that the metallic
portion of the positive part of the casing (the part containing
silver chromate) is made of steel of the type known as "stainless",
containing at least 11% of chromium. On the other hand, the
negative part which is not in contact with highly reactive
materials, may be made of ordinary steel or of another alloy.
The stainless steel used for the positive part of the casing may
contain, besides chromium, nickel in variable proportions.
The invention will be better understood by reference to the
following examples illustrated by the single accompanying FIGURE
which is a cross-sectional view of a cell embodying the
invention.
DETAILED DESCRIPTION
Referring to the drawing, a primary cell 1 of the button type is
shown in which the active materials are lithium and silver
chromate. The casing consists of two cups, the negative material
containing cup 2, the positive material containing cup 3, separated
by a seal ring 4 made of polypropylene or other suitable material.
The negative material containing cup 2 is made from nickel-plated
steel foil and contains a lithium disk or mass 5 constituting the
negative electrode of the cell. The positive mass 6 of the cell
constituted by a mixture of about 99% by weight of silver chromate
and about 1% by weight of carbon black is compressed into the
positive material containing cup 3. The positive and negative
electrodes are separated by a separator made of two constituents;
the constituent 7 made of paper acting as a barrier positioned
against the positive electrode and the constituent 8 made, for
example, of spongy cotton, and more particularly, bearing the
electrolyte (constituted by a molar solution of lithium perchlorate
in propylene carbonate) imbibed therein and positioned against the
lithium disk.
In a first embodiment of the cell 1 according to the invention, the
positive material containing cup 3 was made of stainless steel
containing about 12.5% by weight of chromium without nickel. In a
second example, the cup 3 was made of stainless steel containing
about 17% chromium, also without nickel. In a third example, the
cup 3 was made of stainless steel containing about 18% chromium and
about 9% nickel. It has been observed that in these three examples,
the cells have been preserved without any trace of corrosion during
several months of storage. In contrast, in a cell not according to
the invention in which the cup 3 was made of a steel containing
5.5% chromium, traces of corrosion appear well before the end of
the same storage period.
While specific embodiments of the invention have been disclosed
herein, variations in practice within the scope of the appended
claims are possible and are contemplated. There is no intention,
therefore, of limitations to the exact disclosure hereinabove
presented.
* * * * *